Method for manufacturing carbon fibers and electron emitting device using the same

ABSTRACT

To provide an ink for producing a catalyst capable of stably forming metal particles which act as catalysts suitable for growth of carbon fibers by applying them onto a substrate. 
     A solution containing a metal organic compound containing any one metal of Pd, Fe, Co and Ni and a water-soluble polymer compound is formed by using water or an organic solvent as a main solvent.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for manufacturing carbonfibers and method for manufacturing an electron emitting device usingthe carbon fibers, method for manufacturing a display using the electronemitting device, and an ink for producing a catalyst for use in thesemethods.

2. Description of the Related Art

A field emission-type (FE-type) electron emitting device, whereinelectrons are emitted from a metal surface by applying a strong electricfield of 10⁶ V/cm or more toward a metal, has attracted attention as oneof cold cathode electron-emitting devices. The practical use of theFE-type cold cathode electron-emitting device may enable realization ofan emissive thin display device and contribute reduction of powerconsumption and weight saving.

FIG. 7 shows the structure of a vertical FE-type electron emittingdevice. In the FIG., 71 refers to a substrate; 72 to a extractionelectrode (gate electrode); 73 to a cathode electrode; 74 to aninsulating layer; 75 to an emitter. 76 to a positive electrode (anode)and 77 to a shape of an electron beam irradiated to a positive electrode76. It has a structure (hereinafter referred to as Spindt type) whereinan opening is formed in a stack of the insulating layer 74 and theextraction electrode 72 arranged on the cathode electrode 73 and aconical emitter 75 is arranged in the opening (for example, see C. A.Spindt, “Physical Properties of thin-film field emission cathodes withmolybdenum cones”, J. Appl. Phys., 47, 5248 (1976)).

In addition, as an example of a lateral FE-type electron emittingdevice, there may be mentioned a device wherein an emitter having anacute tip and a extraction electrode extracting (drawing) out anelectron from the emitter tip are formed parallel to a substrate and acollector (called as an anode in the present case) is constituted in theorthogonal direction toward the direction that the extraction electrodeand the emitter face each other.

Furthermore, an electron emitting device using fibrous carbon has beenproposed (for example, see Japanese Patent Application Laid-Open No.H08-115652, Japanese Patent Application Laid-Open No. 2000-223005, andEuropean Patent Laid-Open No. 1022763).

As a method for manufacturing carbon fibers on the substrate, there is amethod for manufacturing the same by disposing catalyst particlescomprising a metal on the substrate and thermally decomposing a carboncompound such as a hydrocarbon using the catalyst particles as nuclei.As a method for disposing said catalyst particles onto the substrate,there is known a method of directly forming a catalyst metal by adepositing technology, e.g., a sputtering method. Also, a method ofusing a metal complex (for example, see Japanese Patent No. 2903290) anda method of using a metal nitrate or a metal chloride have been reported(for example, see Japanese Patent Application Laid-Open No. H03-260119)

SUMMARY OF THE INVENTION

A method of applying a solution of a metal compound dissolved in asolvent as a method for arranging a metal as a catalyst on a substrateis an advantageous process in the case of, for example, forming anelectronic device using carbon fibers on a substrate having a large areasince the process does not require a vacuum apparatus as compared with amethod of direct deposition such as a sputtering method.

However, in the case of the application as a solution onto thesubstrate, a problem that particles are not stably formed after bakingand reduction has arisen in the method of applying a solution in whichonly a metal compound is dissolved. Moreover, in the case of baking aninorganic salt such as a nitrate or a chloride, there is a possibilityof generating a corrosive gas to damage the apparatus and the like.

Therefore, there is existed a problem that it is difficult to stablyform catalyst particles for growing carbon fibers by a solution-applyingmethod.

Namely, in order to manufacture carbon fibers to be applied to anelectronic device including an electron emitting device as arepresentative, it is desired to develop a method for stably formingcatalyst particles on a substrate without requiring any complex process.

An object of the present invention is to provide a method formanufacturing carbon fibers efficiently in a good yield ratio using anink for producing a catalyst capable of stably forming metal-containingparticles on a substrate, the particles acting as a catalyst suitablefor growing the carbon fiber. Another object of the present invention isto provide a method for manufacturing an electronic device such as anelectron emitting device having the carbon fibers and a method formanufacturing a display comprising the electron emitting device.

The invention has been accomplished as a result of extensive studies forsolving the above-mentioned problem. The invention includes thefollowing constitutions.

According to one aspect of the present invention, there is provided amethod for manufacturing carbon fibers comprising:

a step of forming a coated film containing a metal organic compound anda polymer compound by applying an ink for producing a catalystcomprising a solution containing at least the metal organic compound andthe polymer compound onto a substrate,

a step of forming catalyst particles comprising a metal constituting theabove metal organic compound by heating the above coated film, and

a step of forming carbon fibers by bringing a gas containing carbon intocontact with the above catalyst particles.

According to another aspect of the present invention, there is provideda method for manufacturing an electron emitting device containing carbonfibers connected to an electrode, comprising:

a step of forming a coated film comprising a metal organic compound anda polymer compound by applying an ink for producing a catalystcomprising a solution containing at least the metal organic compound andthe polymer compound onto the electrode,

a step of forming catalyst particles comprising a metal constituting themetal organic compound on the electrode by heating the coated film, and

a step of forming carbon fibers by bringing a gas containing carbon intocontact with the above catalyst particles.

In the above method for manufacturing carbon fibers and the above methodfor manufacturing an electron emitting device according to theinvention, the following constitutions are included as preferredembodiments.

1) The polymer compound is a water-soluble polymer compound. Inparticular, the polymer compound is any one of polyvinyl alcohol,polyacrylic acids and polyvinylpyrrolidone.

2) The metal constituting the metal organic compound is any one of Pd,Fe, Co and Ni.

3) The metal organic compound is a metal organic complex.

4) A main solvent of the catalyst-manufacturing ink is water or anorganic solvent.

5) The step of heating the coated film is carried out in a non-oxidizingatmosphere. Alternatively, the step is carried out by baking the coatedfilm in an oxidizing atmosphere and then heating it in a reducingatmosphere.

6) The gas containing carbon is a hydrocarbon gas or a mixed gas of ahydrocarbon gas with hydrogen gas.

According to a further aspect of the present invention, there isprovided an ink for producing a catalyst for growing carbon fibers,comprising at least a metal organic compound, a polymer compound and asolvent.

In the above catalyst-manufacturing ink according to the invention, thefollowing constitutions are included as preferred embodiments.

1) The polymer compound is a water-soluble polymer compound. Inparticular, the polymer compound is any one of polyvinyl alcohol,polyacrylic acids and polyvinylpyrrolidone.

2) The metal constituting the metal organic compound is any one of Pd,Fe, Co and Ni.

3) The metal organic compound is a metal organic complex.

4) A main solvent of the catalyst-manufacturing ink is water or anorganic solvent.

According to still another aspect of the present invention, there isprovided a method for manufacturing a display using a plurality ofelectron emitting elements, wherein the electron emitting elements aremanufactured by the method of the above second aspect of the invention.

According to the present invention, catalyst particles for growingcarbon fibers can be stably formed by applying an ink for producing acatalyst containing a metal organic compound and a polymer compound ontoa substrate, followed by heating. An electron emitting element grownfrom the catalyst particles and containing carbon fibers connected to anelectrode exhibits a satisfactory electron emitting characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, 1C, 1D and 1E illustrate one example of the process formanufacturing an electron emitting element of the invention.

FIGS. 2A and 2B illustrate one example of the electron emitting elementof the invention.

FIG. 3 illustrates a state at the time when the electron emittingelement of FIGS. 2A and 2B is operated.

FIG. 4 illustrates an electron emitting characteristic of the electronemitting element according to the invention.

FIGS. 5A, 5B and 5C are schematic illustrations of structure of carbonnanotubes.

FIGS. 6A, 6B, 6C-1 and 6C-2 are schematic illustrations of structure ofgraphite nanofibers.

FIG. 7 illustrates a conventional vertical FE-type electron emittingelement.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following will describe the method for manufacturing carbon fibersand the method for manufacturing an electron emitting device as oneexample of electronic devices, and the catalyst-manufacturing ink foruse in these methods according to the invention with reference toEmbodiments. However, sizes, materials and shapes of the constitutingparts and a relative position thereof described below should not beconstrued to limit the scope of the invention thereto. Also, the methodfor manufacture is not limited to the steps described below.

In this invetion, the “carbon fiber” or “fiber mainly composed ofcarbon” in the present invention. includes a carbon nanotube “hollowfiber”, a graphite nanofiber (referring to a “fiber constituted bystacking graphenes in the axial direction of the fiber” or a “carbonfiber constituted by stacking a large number of graphenes having c-axiswhich is not perpendicular to the fiber axis” including a cup stacktype), a carbon nanocoil (a spiral carbon fiber), carbon nanohorn(carbon fibers wherein one end of a carbon nanotube is closed), and anamorphous carbon fiber.

Moreover, the catalyst particles comprising a metal in the presentinvention. include not only particles composed of the metal alone butalso particles mainly composed of the metal.

First, there is described the method for manufacturing carbon fibers ofthe invention using the catalyst-manufacturing ink of the invention.

In the method for manufacturing carbon fibers of the invention, an inkfor producing a catalyst comprising a solution containing at least ametal organic compound and a polymer compound is applied onto asubstrate.

It is to be noted that the “catalyst-manufacturing ink” in the presentinvention. means a liquid containing raw materials for forming desiredcatalyst particles but conceptually does not exclude a liquid having afunction or purpose other than the formation of catalyst particles.

In the present invention, the metal constituting the metal organiccompound contained in the catalyst-manufacturing ink is preferably ametal selected from noble metals such as palladium, platinum, rhodium,iridium, ruthenium and osmium, and first transition metals such astitanium, vanadium, chromium, manganese, iron, cobalt and nickel.

As the metal organic compounds containing the above noble metals,specifically, the metal organic compounds containing palladium includepalladium acetylacetonates, palladium carboxylates such as palladiumacetate, and the like, the metal organic compounds containing platinuminclude platinum acetylacetonates, platinum carboxylates such asplatinum acetate, and the like, the metal organic compounds containingrhodinum include rhodium acetylacetonates, rhodium carboxylates such asrhodium octylate (dimer) and rhodium acetate (dimer), and the like, themetal organic compounds containing iridium include iridiumacetylacetonates and the like, the metal organic compounds containingruthenium include ruthenium acetylacetonates and the like, and the metalorganic compounds containing osmium include osmium acetylacetonates andthe like.

As the metal organic compounds containing the above first transitionmetals, specifically, the metal organic compounds containing titaniuminclude titanium acetylacetonates, titanium oxide acetylacetonates andthe like, the metal organic compounds containing vanadium includevanadium acetylacetonates, vanadium oxide acetylacetonates and the like,the metal organic compounds containing chromium include chromiumacetylacetonates, chromium carboxylates such as chromium acetate, andthe like, the metal organic compounds containing manganese includemanganese acetylacetonates, manganese carboxylates such as manganeseacetate, manganese formate and manganese benzoate, and the like, themetal organic compounds containing iron include iron acetylacetonates,iron carboxylates such as iron acetate, iron octylate, iron stearate andiron oxalate, and the like, the metal organic compounds containingcobalt include cobalt acetylacetonates, cobalt carboxylates such ascobalt acetate, cobalt naphthenate and cobalt oxalate, and the like, themetal organic compounds containing nickel include nickelacetylacetonates, nickel carboxylates such as nickel acetate, nickelformate and nickel stearate, and the like, the metal organic compoundscontaining copper include copper acetylacetonates, copper carboxylatessuch as copper acetate and copper benzoate, and the like. In addition,the metal organic compounds of the first transition metals also includemetal carbonyl compounds, alkoxy metal compounds, cyclopentadienyl metalcompounds and the like but these compounds are apt to be influenced bymoisture, so that it is necessary to use an anhydrous organic solvent orthe like when the compounds are used.

The above metal organic compound containing a noble metal or a firsttransition metal may be an organic complex to which a ligandcoordinates. The ligand includes a compound coordinating with an oxygen(O) atom, a compound coordinating with an nitrogen (N) atom, or thelike, but, preferred is a compound coordinating with a nitrogen (N)atom, such as amines, alcohol amines or ethylenediamines.

Among the above noble metals and first transition metals, palladium,iron, cobalt and nickel are preferably used as the metals constitutingthe metal organic compounds of the invention.

In particular, as the metal organic compounds containing palladium,preferred are palladium acetylacetonate, palladium carboxylates and thelike.

Moreover, the palladium carboxylates may be coordinated by an amineligand. For example, a compound coordinated by ammonia, ethanolamine,ethylenediamine or the like is also preferred.Tetra(monoethanolamine)palladium acetate or the like is a preferredcompound for an aqueous system.

As the metal organic compounds containing iron, cobalt, or nickel,preferred are iron acetylacetonate, cobalt acetylacetonate, nickelacetylacetonate, iron alkylcarboxylates, cobalt alkylcarboxylates,nickel alkylcarboxylates and the like.

Furthermore, for carboxylates, also preferred is an amine ligand, forexample, a compound coordinated by a nitrogen atom of ammonia,ethanolamine, ethylenediamine and the like. Moreover, a concentrationrange of the metal in the metal organic compound for use in the presentinvention. somewhat varies depending on the kind of the metal organiccompound to be used, but is preferably from 0.005% to 1% by weight basedon the weight of the solution (ink for producing catalyst). Too lowmetal concentration may invite too small amount of metal fine particles,and too high metal concentration tends to result in a metal film. Thus,it becomes difficult to form catalyst particles on a substrate.

Next, the polymer compound to be contained in the catalyst-manufacturingink will be described.

In the present invention, the catalyst particles comprising a metal(particles mainly composed of the metal) can be stably formed byapplying an ink for producing a catalyst which is a solution containinga metal organic compound and a polymer compound onto a substrate,followed by baking and reduction. This is because effects of the polymercompound have appeared at the application of the ink. The situationwhere the solvent is removed by drying after the application resemblesthe situation at an operation for recrystalization which is a method forpurifying a solid compound. This is a situation where crystals of themetal organic compound in the metal organic compound may be precipitatedon the substrate as large particles. However, since the polymer compoundis present in the solution, the metal organic compound cannot freelymove by the action of the polymer compound even when the metal organiccompound is dispersed or the solvent is dried, and thus the metalcompound remains dispersed. Therefore, discrete catalyst particles canbe formed after baking and reduction.

The polymer compound according to the invention is preferably awater-soluble polymer compound. This is because a functional group forachieving the water solubility tends to interact with the metal organiccompound and also with the substrate, and hence the functional groupmakes it easy to disperse the organic compound. As the water-solublepolymer compound, preferred are polyvinyl alcohol, polyvinylpyrrolidoneand polyacrylates. The polyvinyl alcohol for use in the presentinvention, may contain polyvinyl alcohol partially esterified. Degree ofpolymerization of the water-soluble polymer compound is preferably inthe range of 400 to 2000. When the degree of polymerization is smallerthan the range, the metal organic compound is difficult to dispersesufficiently and when the degree of polymerization is larger than therange, viscosity of the solution becomes too high, and there arises aproblem in its application. In order to disperse the metal organiccompound without resulting in too high solution viscosity, it ispreferable to use a polymer compound whose degree of polymerization isfrom 400 to 2000. The concentration of the water-soluble polymercompound for use in the present invention. is preferably from 0.01 to0.5% by weight. When the compound is used within the range, a gooddispersibility of the metal organic compound is achieved.

As the solvent for the catalyst-manufacturing ink of the invention,either water or an organic solvent can be preferably used as a mainsolvent. As the organic solvent to be used as the main solvent, use canbe made of a solvent such as an alcohol such as methanol, ethanol,1-propyl alcohol, 2-propyl alcohol, 2-butanol; an aromatic solvent suchas toluene; or N-methylpyrrolidone, N,N-dimethylacetamide,N,N-dimethylformamide, dimethyl sulfoxide, or the like. These solventsmay be used solely or as a mixture of two or more of them.

Moreover, as the solvent for the ink, in an aqueous solvent, an alcoholcan be further added. As an alcohol to be added, use can be made of amonohydric alcohol mentioned in the above as the main solvent or apolyhydric alcohol such as ethylene glycol, propylene glycol, diethyleneglycol glycerin and the like. The addition of such an alcohol maysometimes improve wettability.

In the method for producing carbon fibers of the invention, as themethod of applying the above catalyst-manufacturing ink onto asubstrate, a usual applying method such as spin coating, dipping, spraycoating and the like can be employed. As other applying methods, liquiddrop-applying methods including an ink-jet method such as a piezo systemor a heating and bubbling system (bubble-jet, a registered trademark) asa representative can be also employed. The ink-jet method is preferablyemployed since a desired amount can be selectively imparted to a desiredregion. By these methods, a coated film containing the metal organiccompound and the polymer compound is formed on a substrate.

Then, by heating (baking) the above coated film, catalyst particlescomprising the metal constituting the metal organic compound containedin the ink is formed. The heating step will be described below.

For the heating step of forming catalyst particles comprising the metalconstituting the metal organic compound by heating the coated filmcontaining the metal organic compound and the polymer compound, a methodof conducting in a non-oxidizing atmosphere and a method of heating in areductive atmosphere after baking the coated film in an oxidizingatmosphere may be mentioned. In case where a polymer is removed, heatingin an oxidizing atmosphere is preferable.

In the method of conducting in a non-oxidizing atmosphere, catalystparticles comprising the metal constituting the metal organic compoundare formed through thermal decomposition of the metal organic compoundby heating it under vacuum at about 500° C. to 700° C.

In the method of heating in a reductive atmosphere after baking thecoated film in an oxidizing atmosphere, catalyst particles comprisingthe metal constituting the metal organic compound are formed by bakingthe metal organic compound at about 200° C. to 500° C., preferably about350° C. to convert it into corresponding metal oxide and then reducingit under a hydrogen atmosphere at about 500° C. to 700° C.

After the catalyst particles are formed by heating the coated film,carbon fibers are grown using the catalyst particles. Namely, carbonfibers are formed by bringing a gas containing carbon into contact withthe catalyst particles and simultaneously heating them. In other words,the carbon fiber is grown by bringing a gas containing carbon intocontact with the catalyst particle, whose catalytic function is beingactivated. Typically, the carbon fiber can be grown by bringing a gascontaining carbon into contact with the catalytic particle disposed onthe base member which is being heated.

As the gas containing carbon for use in the present invention, ahydrocarbon gas such as acetylene, ethylene, methane, propane orpropylene is preferably used, but the gas may be a vapor of an organicsolvent such as ethanol or acetone. Moreover, a mixed gas of the abovehydrocarbon gas with hydrogen gas is also preferably used. In the casethat the mixed gas is used, when the coated film is baked in anoxidizing atmosphere, e.g., in the air, carbon fibers can be grown in amixed gas stream of the hydrocarbon gas with hydrogen gas, withouttaking out a substrate, under a reduction treatment in a hydrogen gasstream with further flowing the hydrogen gas.

FIGS. 5A to 5C and 6A to 6C-2 show schematic illustrations of carbonfibers formed by decomposing a hydrocarbon gas using the above catalystparticles according to the invention. Each of FIGS. 5A and 6A shows amorphologic feature observed at an optical microscope level (themagnification of up to 1000).

Each of FIGS. 5B and 6B shows a morphologic feature observed at ascanning electron microscope (SEM) level (the magnification of up to30,000) and is an enlarged view of 51 and 61 in FIGS. 5A and 6A,respectively. Each of 5C, 6C-1 and 6C-2 shows a morphologic feature ofcarbon observed at a transmission electron microscope (TEM) level (themagnification of up to 1,000,000). FIG. 5C schematically illustrates anenlarged view of 52 in FIG. 5B, FIGS. 6C-1 schematically illustrates anenlarged view of 62 in FIG. 6B, and FIGS. 6C-2 schematically illustratesan enlarged view of 63 in FIG. 6B.

As shown in FIGS. 5A to 5C, the fiber wherein the 53 has a morphologicfeature of cylindrical shape (the fiber having a multi-structuredcylindrical shape of graphene is called a multi-wall nanotube) is calleda carbon nanotube. In particular, when a tip of the tube has an openedstructure, it exhibits the lowest threshold level.

Alternatively, FIGS. 6A to 6C-2 schematically illustrate the carbonfibers formed at a relatively low temperature similarly using a catalystas in the case of the carbon nanotube. This type of carbon fiber(sometimes called a “graphite nanofiber”) is constituted by stackedgraphenes 64 in the axis direction of the fiber.

Either carbon fiber has a threshold level for electron emission of about1 to 10 V/μm and has preferable characteristics as an electron emittingmaterial. However, since the graphite nanofiber is superior in anelectron emitting ability to the carbon nanotube, it is preferable toselect the graphite nanofiber for an electron emitting device havingcarbon fibers.

The following will describe an electron emitting device using the carbonfiber obtained by the invention in detail with reference to FIGS. 1A,1B, 1C, 1D, 1E, 2A and 2B.

FIG. 2A is a schematic illustration showing one example of structure ofthe electron emitting device according to the invention and FIG. 2B is across-sectional view at 2B—2B in FIG. 2A. FIGS. 2A and 2B is a drawingafter carbon fibers are grown using catalyst particles.

In FIGS. 1A, 1B, 1C, 1D, 1E, 2A and 2B, reference 11 denotes aninsulating substrate; reference 12 denotes second electrode (extractionelectrode (gate electrode) for. extracting electrons from the fiber, orcontrol electrode for controlling electrons emitted from the fiber);reference 13 denotes first electrode (cathode electrode); reference 14denotes a resist pattern; reference 15 denotes a conductive materiallayer; reference 16 denotes catalyst particles; reference 17 denotescarbon fibers which are materials for an emitter. Note that theconductive material layer 15 is not always necessary. In this example,the conductive material layer 15 where the first electrode 13 andcatalyst particles 16 are arranged has a stacked structure, but it issufficient for the layer to have a morphologic feature where catalystparticles 16 are exposed on the surface of the negative electrode 13.Namely, a morphologic feature where the first electrode 13 has catalystparticles 16 is also possible.

As the insulating substrate 1, an insulating substrate such as silicaglass whose surface is thoroughly washed may be mentioned.

The second electrode 12 and the first electrode 13 are conductive andare formed by a general vacuum film-forming technology such as vapordeposition, sputtering and the like, a photolithography technology orthe like. The material is desirably a heat-resistant material such ascarbon, a metal, a metal nitride or a metal carbide.

The carbon fiber 17 is a carbon fiber such as a carbon nanotube orgraphite nanofiber grown using catalyst particles 16 of FIGS. 1A to 1E(namely, catalyst particles obtained by forming a coated film containinga metal organic compound and a polymer compound by applying an ink forproducing a catalyst containing the metal organic compound and thepolymer compound and heating (baking) the above coated film).

The following will describe one example of the process for producing theelectron emitting element shown in FIGS. 2A and 2B with reference toFIGS. 1A to 1E.

(Step 1)

After the substrate 11 is thoroughly washed, an electrode layer having athickness of 500 nm (not shown in the Figure) is first formed all overthe substrate by sputtering or the like in order to form the drawerelectrode 12 and the negative electrode 13.

Next, in a photolithographic step, a resist pattern is formed using apositive photoresist (not shown in the Figure). Then, using the abovepatterned photoresist as a mask, the electrode layer is subjected to adry etching using Ar gas to pattern the second electrode 12 and firstelectrode (cathode electrode) 13 having a gap between the electrodes(gap width) of 5 μm (FIG. 1A).

Hereinafter, the patterning of the thin layers and resists by aphotolithography technology, film formation, lift-off, etching, and thelike are simply referred to as “patterning”.

(Step 2)

In a photolithographic step, the resist pattern 14 is formed using anegative photoresist to be used for successive lift-off of an upperlayer (FIG. 1B).

Next, therein is formed a conductive material layer (TiN is usedtherein) wherein carbon fibers 17 are grown using catalyst particles 16.Then, the catalyst-manufacturing ink is applied therein with rotation toform a coated film containing a metal organic compound and a polymercompound and then the film is heated to form catalyst particles 16 ofthe metal (FIG. 1C). In case where a polymer is removed, the abovecoated film is preferably heated in an oxidizing atmosphere. Further,when the areas of catalyst particles to be disposed are patterned(especially, when the patterning is carried out by a wet process), it ispreferable to pattern the catalyst particles oxidized by heating thecoated film in an oxidation atmosphere and then reduce the oxidizedparticles by heating them, for example, in a reduced gas atmosphere.Thus, the loss of a material constituting the catalyst particles with apeeling agent and solvent patterning can be suppressed. According to theinvention, by adding a polymer, distance between neighboring catalystparticles can be arbitrarily controlled. Therefore, growth of carbonfibers using catalyst particles formed according to the inventionresults in control of the distance between carbon fibers. As a result,in the case that a large number of carbon fibers are grown on the firstelectrode 13 and are used as an electron emitting device, an electricfield can be sufficiently applied to the individual carbon fibers andgood electron emitting characteristics can be realized.

(Step 3)

Using a removing liquid (remover) for the resist patterned in Step 2,the conductive material layer 15 and catalyst particles 16 on the resistare lifted off together with the resist and a pattern of the conductivematerial layer 15 and catalyst particles 16 is left in a desired region(FIG. 1D).

When a photosensitive material is further added to the ink for producingcatalyst or when the photosensitivity is given to a polymer included inthe ink for producing catalyst, after coated on the substrate with thepreviously patterned conductive material layer, the desirably patternedcoated film comprising an organic compound and polymer is formed by theconventional photolithography techniques in which exposure anddevelopment are carried out using a mask. Next, a heating step iscarried out in a non-oxidizing atmosphere, or a heating step is carriedout in an oxidizing atmosphere and then a heating step is carried in areducing atmosphere, to form catalyst particle pattern on the desiredareas. Although the above heating step may be carried out in anon-oxidizing atmosphere, in case where a polymer is removed, baking inan oxidizing atmosphere is preferable.

(Step 4)

Subsequently, the product is subjected to a thermal decomposition(thermal CVD) treatment in a stream of a gas containing carbon. Then,when it is observed on a scanning electron microscope, it is found thata large number of carbon fibers are formed (FIG. 1E).

The following will describe the thus manufactured electron emittingdevice using the carbon fibers with reference to FIGS. 3 and 4.

The device equipped with the second electrode (gate electrode) 12 andthe cathode electrode 13 having a gap between them of several μm, asshown in FIGS. 2A and 2B, is placed in a vacuum apparatus 38 as shown inFIG. 3 and the apparatus is thoroughly evacuated until the pressurereaches about 10⁻⁴ Pa by a vacuum evacuating apparatus 39. As shown inFIG. 3, using a high voltage source, a positive electrode (anode) 30 isprovided at a position having a height H of several mm from thesubstrate and a high voltage of several kilo volts is applied.

In this connection, a fluorescent material 31 covered with a conductivefilm is provided to the anode electrode 30.

To the device (between the cathode electrode 13 and the gate electrode12) is applied a pulse voltage of about several tens voltage as adriving voltage V_(f), whereby a device current I_(f) and an electronemission current I_(e) are measured.

At that time, an equipotential line 32 is formed as shown in FIG. 3, andthe point to which the electric field is most concentrated is assumed tobe a place of the electron emitting materials (carbon fibers) nearest tothe positive electrode 30 shown by 33 and inside of the gap.

It is considered that electrons are emitted from the place to which theelectric field is most concentrated among the electron emittingmaterials positioned in the vicinity of the electric field-concentratedpoint.

The I_(e) characteristic of the device was as shown in FIG. 4.

By arranging a plurality of the above electron emitting devices, a gooddisplay can be constructed.

EXAMPLES

The following will describe Examples of the invention in detail.

Example 1

Following the steps shown in FIGS. 1A to 1E, an electron emitting devicewas manufactured.

(Step 1)

After an quartz substrate used as the substrate 11 is thoroughly washed,first, an underlying Ti having a thickness of 5 nm and Pt having athickness of 100 nm not shown in the Figure were continuouslyvapor-deposited onto all over the substrate by sputtering in order toform the etraction electrode 12 and the cathode electrode 13.

Next, in a photolithographic step, a resist pattern is formed using apositive photoresist not shown in the Figure.

Then, using the above patterned photoresist as a mask, the Pt and Tilayers were subjected to a dry etching using Ar gas to pattern theextraction electrode 12 and cathode electrode 13 having a gap betweenthe electrodes (gap width) of 5 μm.

(Step 2)

In a photolithographic step, a resist pattern 14 is formed using anegative photoresist to be used for subsequent lift-off of an upperlayer. Next, a TiN layer was formed as the conductive material layer 15.

An ink for producing a catalyst was prepared by mixing 0.44 g oftetrakis(monoethanolamine)palladium acetate, 0.05 g of polyvinylalcohol, 25 g of isopropyl alcohol, and 1 g of ethylene glycol andmaking the whole amount 100 g by addition of water. The ink wasspin-coated onto the above TiN layer and baked at 350° C. for 30 minutesin the air, and then the resulting ink was subjected to a reductiontreatment at 600° C. in a hydrogen stream to form catalyst particles 16.When the particles were observed on a scanning electron microscope(SEM), Pd particles were formed on the TiN layer.

(Step 3)

Using a removing liquid for the resist patterned in Step 3, theconductive material layer 15 and catalyst particles 16 on the resist arelifted off together with the resist and a pattern of the conductivematerial layer 15 and catalyst particles 16 was left in a desiredregion.

(Step 4)

Subsequently, a thermal treatment was carried out in an ethylene stream.Then, when it was observed on a scanning electron microscope, it isfound that a large number of carbon fibers 17 were formed.

The electron emitting device manufactured as above was placed in avacuum apparatus 38 as shown in FIG. 3 and the apparatus was thoroughlyevacuated until the pressure reached 2×10⁻⁵ Pa by a vacuum evacuatingapparatus 39. A voltage V_(a) of 10 kV is applied to the positiveelectrode 30 apart from the device by H=2 mm. At that time, to thedevice was applied a pulse voltage of a driving voltage V_(f) of 20 V,whereby a device current I_(f) and an electron emission current I_(e)were measured.

I_(f) and I_(e) characteristics of the device were those as shown inFIG. 4. Namely, I_(e) rapidly increased from about a half of the appliedvoltage and when V_(f) was 15V, an electron emission current I_(e) ofabout 1 μA was observed. On the other hand, I_(f) was similar to theI_(e) characteristic but the value was found to be a value smaller thanthat of I_(e) by one order or more.

Example 2

An electron emitting device was manufactured in the same manner as inExample 1 with the exception that Step 2 was carried out as follows, andI_(f) and I_(e) thereof were measured.

(Step 2)

In a photolithographic step, a resist pattern 14 is formed using anegative photoresist to be used for subsequent lift-off of an upperlayer. Next, a TiN layer was formed as the conductive material layer 15.

An ink for producing a catalyst was prepared by mixing 0.42 g of cobaltacetate tetrahydrate, 0.05 g of polyvinyl alcohol, 25 g of isopropylalcohol and 1 g of ethylene glycol and making the whole amount 100 g byaddition of water. The ink was spin-coated onto the TiN layer and bakedat 350° C. for 30 minutes in the air. According to the above steps, thecobalt oxide particles are produced. Next, the conductive material layer15 and oxide particles on the resist 14 are lifted off with a peelingliquid for the resist, and then a heating process is carried out at 600°C. in a hydrogen stream to reduce the cobalt oxide particles to themetal cobalt particles.

When the particles were observed on a scanning electron microscope(SEM), Co particles were formed on the TiN layer. A heating process isfurther carried out in an ethylene stream to produce a carbon fiber fromcobalt particles. In this working example, since elution into a peelingliquid is more suppressed by patterning the oxidized cobalt, a reducingprocess was carried out after patterning the oxidized particles.

I_(f) and I_(e) characteristics of the resulting electron emittingdevice were those as shown in FIG. 4. Namely, I_(e) rapidly increasedfrom about a half of the applied voltage and when V_(f) was 15V, anelectron emission current I_(e) of about 1 μA was observed. On the otherhand, I_(f) was similar to the I_(e) characteristic but the value wasfound to be a value smaller than that of I_(e) by one order or more.

Example 3

An electron emitting device was manufactured in the same manner as inExample 1 with the exception that Step 2 was carried out as follows, andI_(f) and I_(e) thereof were measured.

(Step 2)

In a photolithographic step, a resist pattern 14 is formed using anegative photoresist to be used for subsequent lift-off of an upperlayer. Next, a TiN layer was formed as the conductive material layer 15.

An ink for producing a catalyst was prepared by mixing 0.42 g of nickelacetate tetrahydrate, 0.05 g of polyacrylic acid, 25 g of isopropylalcohol and 1 g of ethylene glycol and making the whole amount 100 g byaddition of water. The ink was spin-coated onto the TiN layer and bakedat 350° C. for 30 minutes in the air, and then the resulting ink wassubjected to a reduction treatment at 600° C. in a hydrogen stream toform catalyst particles. When the particles were observed on a scanningelectron microscope (SEM), Ni particles were formed on the TiN layer.

I_(f) and I_(e) characteristics of the resulting electron emittingdevice were those as shown in FIG. 4. Namely, I_(e) rapidly increasedfrom about a half of the applied voltage and when V_(f) was 15V, anelectron emission current I_(e) of about 1 μA was observed. On the otherhand, I_(f) was similar to the I_(e) characteristic but the value wasfound to be a value smaller than that of I_(e) by one order or more.

Example 4

An electron emitting device was manufactured in the same manner as inExample 1 with the exception that Step 2 was carried out as follows, andI_(f) and I_(e) thereof were measured.

(Step 2)

In a photolithographic step, a resist pattern 14 is formed using anegative photoresist to be used for subsequent lift-off of an upperlayer. Next, a TiN layer was formed as the conductive material layer 15.

An ink for producing a catalyst was prepared by mixing 0.63 g of ironacetylacetonate and 0.06 g of polyvinylpyrrolidone and making the wholeamount 100 g by addition of ethanol. The ink was spin-coated onto theTiN layer and subjected to a thermal treatment at 600° C. under vacuum.When the product was observed on a scanning electron microscope (SEM),Fe particles were formed on the TiN layer.

I_(f) and I_(e) characteristics of the resulting electron emittingdevice were those as shown in FIG. 4. Namely, I_(e) rapidly increasedfrom about a half of the applied voltage and when V_(f) was 15V, anelectron emission current I_(e) of about 1 μA was observed. On the otherhand, I_(f) was similar to the I_(e) characteristic but the value wasfound to be a value smaller than that of I_(e) by one order or more.

According to the invention, catalyst particles for growing carbon fibersare obtained on a substrate without requiring any complex process andcarbon fibers are satisfactorily grown from the catalyst particles.Also, the electron emitting device using the carbon fibers achieves goodelectron emitting characteristics. Moreover, according to the invention,distance between individual carbon fibers can be increased and as aresult, an electric field can be sufficiently applied to the individualcarbon fibers. Accordingly, an electron emitting device having excellentelectron emitting characteristics can be efficiently manufactured andfurthermore, a display using the electron emitting device can beefficiently provided.

1. A method for manufacturing carbon fiber, comprising: a step offorming a coated film containing a metal organic compound and awater-soluble polymer compound by applying an ink for producing acatalyst comprising a solution containing at least the metal organiccompound and the polymer compound onto a substrate, a step of formingcatalyst particles comprising a metal constituting said metal organiccompound by heating said coated film, and a step of forming carbonfibers by bringing a gas containing carbon into contact with thecatalyst particles.
 2. The method according to claim 1, wherein saidpolymer compound is any one selected from the group consisting ofpolyvinyl alcohol, polyacrylic acids and polyvinylpyrrolidone.
 3. Themethod according to claim 1, wherein said metal constituting the metalorganic compound is any one selected from the group consisting of Pd,Fe, Co and Ni.
 4. The method according to claim 1, wherein said metalorganic compound is a metal organic complex.
 5. The method according toclaim 1, wherein a main solvent of said catalyst-manufacturing ink iswater.
 6. The method according to claim 1, wherein a main solvent ofsaid catalyst-manufacturing ink is an organic solvent.
 7. The methodaccording to claim 1, wherein the step of heating said coated film iscarried out in a non-oxidizing atmosphere.
 8. The method according toclaim 1, wherein the step of heating said coated film is a step ofbaking the coated film in an oxidizing atmosphere and then heating it ina reducing atmosphere.
 9. The method according to claim 1, wherein saidgas containing carbon is a hydrocarbon gas.
 10. The method according toclaim 1, wherein said gas containing carbon is a mixed gas of ahydrocarbon gas with hydrogen gas.
 11. A method for manufacturing anelectron emitting device containing carbon fibers connected to anelectrode comprising at least: a step of forming a coated filmcontaining a metal organic compound and a water-soluble polymer compoundby applying an ink for producing a catalyst comprising a solutioncontaining at least the metal organic compound and the water-solublepolymer compound onto the electrode, a step of forming catalystparticles comprising a metal constituting said metal organic compound onsaid electrode by heating said coated film, and a step of forming carbonfibers by bringing a gas containing carbon into contact with thecatalyst particles.
 12. The method according to claim 11, wherein saidpolymer compound is any one selected from the group consisting ofpolyvinyl alcohol, polyacrylic acids and polyvinylpyrrolidone.
 13. Themethod according to claim 11, wherein said metal constituting the metalorganic compound is any one selected from the group consisting of Pd,Fe, Co and Ni.
 14. The method according to claim 11, wherein said metalorganic compound is a metal organic complex.
 15. The method according toclaim 11, wherein said gas containing carbon is a mixed gas of ahydrocarbon gas with hydrogen gas.
 16. A method for manufacturing adisplay using a plurality of electron emitting devices, wherein saidelectron emitting devices are manufactured by the method according toclaim 11.